1. Field of the Invention
The present invention relates to a force-applying input device for applying a force corresponding to a state of operation of an operation unit to the operation unit, and, more particularly, to means for preventing a torque generating unit for applying the force to the operation unit from getting out of control.
2. Description of the Related Art
A force-applying input device which is described below is conventionally known as an input device which is applied to, for example, a vehicle-installed electrical device centralized control system, a steering apparatus, a gearshift apparatus, or a brake system. The force-applying input device comprises an operation unit operated by an operator, a position detecting unit for detecting an operation state of the operation unit, a torque generating unit for applying a force to the operation unit, and a controller for controlling a driving operation of the torque generating unit in order to apply the force corresponding to the operation state of the operation unit to the operation unit. Such a force-applying input device is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-149324 (FIG. 3).
In the force-applying input device, by driving the torque generating unit, various types of forces corresponding to, for example, the operation direction or operation amount of the operation unit can be applied to the operation unit. Therefore, in various types of apparatuses, the operation of the operation unit provides a predetermined operational feel.
In such a force-applying input device, in order to prevent the torque generating unit from getting out of control, that is, to prevent continued movement of the operation unit within its movement range due to vibration of the torque generating unit occurring when the operator takes his/her hand off the operation unit, the following controlling method is used. This method is not a method in which only torque information corresponding to position information output from the position detecting unit is output to the torque generating unit. It is a method in which a combination of the torque information corresponding to the position information and torque information corresponding to the speed of operation of the operation unit calculated from the rate of change of a position signal is output to the torque generating unit. Since, by the torque information corresponding to the speed of operation of the operation unit, the operation of the operation unit provides resistance similar to viscous friction, this torque information is sometimes called viscous friction torque information.
FIG. 5 shows the structure of this type of force-applying input device proposed by the applicant. The force-applying input device mainly comprises an operation unit 1 operated by an operator, an encoder 2 for detecting an operation state of the operation unit 1, a torque generating unit 3 for applying a force to the operation unit 1, and a controller 4 for controlling a driving operation of the torque generating unit 3 in order to apply a predetermined force corresponding to the operation state of the operation unit 1 to the operation unit 1.
The controller 4 comprises a rotational angular speed calculating unit 4a for calculating rotational angular speed information of the operation unit 1 by a signal pulse output from the encoder 2, a torque calculating unit 4b for calculating torque information supplied to the torque generating unit 3, and a rotational angle calculating unit 4f for calculating rotational angle information of the operation unit 1 by the rotational angular speed information output from the rotational angular speed calculating unit 4a. The rotational angular speed calculating unit 4a outputs the calculated rotational angular speed information to the torque calculating unit 4b and the rotational angle calculating unit 4f. The torque calculating unit 4b calculates the torque information based on the rotational angular speed information output from the rotational angular speed calculating unit 4a and the rotational angle information output from the rotational angle calculating unit 4f, and outputs the torque information to the torque generating unit 3. A torque component which is calculated based on the rotational angular speed information corresponds to viscous friction torque, and a torque component which is calculated based on the rotational angle information corresponds to the force applied to the operation unit 1 that provides, for example, a tactile feel.
As shown in FIG. 6, the rotational angular speed calculating unit 4a counts a number n of signal pulses per definite period of time Δt output from the encoder 2, and calculates rotational angular speed information θdot of the operation unit 1 using an expression θdot=Δθ·n/Δt. Δθ in the expression refers to the resolution of the encoder 2.
Accordingly, in the force-applying input device having this structure, the viscous friction torque component based on the rotational angular speed information is added to the torque information supplied to the torque generating unit 3. Therefore, as long as signal pulses output from the encoder 2 can be precisely counted, it is possible to prevent the torque generating unit 3 from getting out of control.
The force-applying input device having the above-described structure is constructed based on the assumption that the rotational angular speed calculating unit 4a can always precisely count the signal pulses output from the encoder 2. However, actually, when the number n of signal pulses per definite period of time Δt is increased due to a high operation speed of the operation unit 1, the signal pulses are miscounted more frequently. Therefore, rotational angular speed information corresponding to the actual rotational angular speed of the operation unit 1 can no longer be calculated. Consequently, the operation of the operation unit 1 becomes unstable, and, in the worst case, the torque generating unit 3 gets out of control.